Bats orient themselves in the environment by emitting ultrasonic cries and detecting echoes of these cries that are reflected from near-by objects. 4) One of the many intriguing questions about echolocation, this active sonar sense used by bats, is whether it can serve for the perception of depth or differences in the distance to targets. Bats must often face situations which involve multiple targets; for example, a cluster of several flying insects or an insect flying near branches. It would be of obvious value to the bat in detecting and identifying objects if its sonar could distinguish among such multiple targets. Depth perception is of theoretical interest to us because we might be able to determine something about how the bat processes echoes if we knew how well it could perceive distance or range. Many of the theories about echolocation and the kinds of information extracted from echoes by bats have been proposed in the form of hypothetical mechanisms for the determination of distance. 1,3,9—18) The experiments to be described here are attempts to measure the acuity of the bat in discriminating differences in distance. Their results identify echo travel time as an important auditory cue for target range and suggest how this cue might be processed in the bat’s auditory nervous system.